1. Field of the Invention:
The present invention relates to a preloader suitable for use with a webbing retractor or the like, for firmly fastening a webbing around an occupant when a vehicle is abruptly decelerated.
2. Description of the Related Art:
In a seat belt system, an occupant is restrained by a webbing when a vehicle is abruptly decelerated. However, the performance of restraint of the occupant by the webbing cannot be sufficiently exhibited when a spacing between the webbing and the occupant is large. Therefore, there has been proposed a webbing retractor provided integrally with a preloader of a type wherein the webbing is firmly applied to the occupant by forcibly pulling the webbing in a webbing winding direction when the vehicle is abruptly decelerated.
In this type of preloader, when the vehicle is abruptly decelerated, a piston is moved along the inside of the cylinder by high pressure gas rapidly generated from a gas generator loaded with an explosive or the like. The movement of the piston is then converted into a rotational force in the webbing winding direction by a clutch means. Afterwards, the rotational force thus converted is transmitted to a webbing take-up shaft so as to wind the webbing on the webbing take-up shaft, thereby firmly applying the webbing to the occupant.
In the preloader, however, the high pressure gas acts on the piston, so that the piston is moved toward the leading end (terminal region of stroke) of the cylinder at a high speed. It is therefore necessary to increase the strength of the leading end of the cylinder.